On Wed 09-01-19 19:26:05, Pankaj Gupta wrote:

quoted

Virtio pmem provides asynchronous host page cache flush
mechanism. We don't support 'MAP_SYNC' with virtio pmem
and ext4.

Signed-off-by: Pankaj Gupta <redacted>

...

quoted

@@ -371,6 +373,13 @@ static int ext4_file_mmap(struct file *file, struct

vm_area_struct *vma)
 	if (!IS_DAX(file_inode(file)) && (vma->vm_flags & VM_SYNC))
 		return -EOPNOTSUPP;
 
+	/* We don't support synchronous mappings with guest direct access
+	 * and virtio based host page cache flush mechanism.
+	 */
+	if (IS_DAX(file_inode(file)) && virtio_pmem_host_cache_enabled(dax_dev)
+						&& (vma->vm_flags & VM_SYNC))
+		return -EOPNOTSUPP;
+

Shouldn't there rather be some generic way of doing this? Having
virtio_pmem_host_cache_enabled() check in filesystem code just looks like
filesystem sniffing into details is should not care about... Maybe just
naming this (or having a wrapper) dax_dev_map_sync_supported()?

Thanks for the feedback.

Just wanted to avoid 'dax' in function name just to differentiate this with real dax.
But yes can add a wrapper: dax_dev_map_sync_supported()

Thanks,
Pankaj